The objective of this study is to test the hypothesis that PAH and Iothalamate administration via intravenous bolus (IVB) provides accurate estimates of effective renal plasma flow (ERPF) and glomerular filtration rate (GFR) as compared with the standard method of continuous infusion (CI) administration. This method will then be used to evaluate the relationship between renal function and hepatic function in normal volunteers and patients with hepatic insufficiency.